Fig. 6. iVAX-derived conjugates elicit FtLPS-specific antibodies and protect mice from lethal pathogen challenge.

(A) Freeze-dried iVAX reactions assembled using detoxified lysates were used to synthesize anti–F. tularensis conjugate vaccines for immunization studies. (B) Groups of BALB/c mice were immunized subcutaneously with PBS or 7.5 μg of purified, cell-free synthesized unmodified or FtO-PS–conjugated carrier proteins. FtO-PS–conjugated MBP^4xDQNAT prepared in living E. coli cells using PCGT was used as a positive control. Each group was composed of six mice except for the PBS control group, which was composed of five mice. Mice were boosted on days 21 and 42 with identical doses of antigen. FtLPS-specific IgG titers were measured by enzyme-linked immunosorbent assay (ELISA) in endpoint (day 70) serum of individual mice (black dots) with F. tularensis LPS immobilized as antigen. Mean titers of each group are also shown (red lines). iVAX-derived conjugates elicited significantly higher levels of FtLPS-specific IgG compared to all other groups (**P < 0.01, Tukey-Kramer post hoc test). (C) IgG1 and IgG2a subtype titers measured by ELISA from endpoint serum revealed that iVAX-derived conjugates boosted production of FtO-PS–specific IgG1 compared to all other groups tested (**P < 0.01, Tukey-Kramer post hoc test). These results indicate that iVAX conjugates elicited a T_H2-biased immune response typical of most conjugate vaccines. Values represent means and error bars represent SEs of FtLPS-specific IgGs detected by ELISA.